1. Field of the Invention
The present invention relates to sharpening devices, and, more particularly, to devices for sharpening the blade of a rotary lawn mower without removing the blade from the mower.
2. Description of the Prior Art
There are several advantages to using a lawn mower with a sharp blade over a lawn mower with a dull blade. These advantages include higher quality of mowing, lower fuel consumption, and, for those rotary mowers which are not self propelled, less resistance to pushing.
One method of sharpening the blade of a lawn mower comprises the use of conventional bench-mounted grinding apparatus. With this method, the blade is removed from the mower, sharpened and then replaced on the mower. The adequacy of sharpening using the above method may be determined by mowing a small portion of grass, and, of course, if the sharpening is inadequate, the time consuming process described above must be repeated. Accordingly, it is desirable both in terms of time and effort to sharpen the blade of a lawn mower without removing it from the mower.
Various techniques have been proposed to accomplish the sharpening of the blade "in situ". For example, in U.S. Pat. Nos. 3,136,107 and 3,225,527 to Spear, sharpening apparatus are disclosed which are mounted on the housing of the mower. In U.S. Pat. No. 3,596,412, Brayman states that these arrangements have disadvantages in that the size of the mower housing must be increased to incorporate the sharpener and that there is difficulty in inspecting the blade to determine if it has been adequately sharpened.
U.S. Pat. No. 3,596,412 to Brayman discloses an apparatus having a base and sharpener mounted for an up and down movement with respect to the base. Brayman states that, as the lawn mower is pushed onto the base, the housing of the lawn mower engages a pusher which, via a turnbuckle arrangement, raises a grinding stone into contact with the blade of the mower. The apparatus disclosed by Brayman appears to be somewhat complex in construction.
Another type of sharpening apparatus is disclosed in U.S. Pat. No. 3,665,658 to Warwick. This apparatus comprises a resiliently deformable body portion provided with an upper abrasive surface. The apparatus is designed to be placed on a level surface, e.g., the ground, and the housing of the lawn mower whose blade is to be sharpened is placed over the apparatus. The blade of the lawn mower thus comes into contact with the sharpening device due to the thickness of the foam. Warwick states that the blade may be sharpened by causing momentary rotations of the blade. Since the device disclosed by Warwick is not designed to sharpen a blade which is continuously rotating, it is believed it would take significantly longer and be a significantly more arduous process to sharpen the blade using the Warwick device than using other devices heretofore discussed.